The magnetic field has a north and a south pole.
It is called a dipole field. The north magnetic pole is located just
off the coast of Antarctica (yes, the north magnetic pole is located
near the south geographic pole.)

Here is a space photo of the Northern and Southern
Auroras of the earth superimposed on a model of earth.

The magnetic field of the earth interacts with charged
particles from the sun to create auroras circling the polar
regions

The magnetic field of the earth is made by a
billion ampere electric current which circulates within the liquid
metal of the outer core of the earth. (The liquid metal outer core
stretches from the solid metal inner core about a quarter of the
radius of the earth to the rocky mantle which begins 1/2 way from the
core to the surface.)

When molten rocks which contain iron, cool in the
presence of a magnetic field they record the magnetic field
direction. We can look at the magnetic field recorded in the rocks
and find out about the magnetic field of the earth in the past, the
paleomagnetic field.

The paleomagnetic field shows that the magnetic
field of the earth has flipped its direction many times. The flipping
of the poles occurs after times of hundreds of thousands of years. It
does not reverse on a regular basis but reverses
chaotically.

The molten rocks spreading from mid ocean ridges
record the flipping of the earths poles as bands of north and south
magnetized rock

Magnetic stripes recorded in volcanic rocks underlying Pacific
Ocean off the northwest coast of the U.S.
Black is south pole up, white is north pole up.

(Twice in the record the field has not flipped for
over 10 million years.)

The flip takes a few thousand years.

The last reversal was 780,000 years
ago.

American Scientist Nov 1996 p 552 "The Reversal of
the Earth's Magnetic Field"

Read what expert magnetic field geologists have to
say about the reversal of the earth's magnetic field. at
http://www.sciam.com/askexpert/geology/geology9/geology9.html

The magnetic field stretches out into space around
the earth, a region known as the Earth's magnetosphere. It traps
charged particle from the sun into two regions known as the Van Allen
radiation belts.

The Planets

All planets with strong magnetic fields rotate
rapidly (at least once every few earth days) and also contain an
electrically conducting liquid.

Planet

relative strength at surface

equator field gauss

conductor in planet

tilt of magnetic axis

Earth

1

0.3

molten nickel iron

10.8 °

Mercury

0.0007

Venus

<0.0004

Mars

<0.0002

Jupiter

20,000

4.28

metallic hydrogen

9.6°

Saturn

600

0.22

metallic hydrogen

<1°

Uranus

50

0.23

water,methane,ammonia

58.6°

Neptune

25

0.14

water,methane,ammonia

47°

Table from the book The New Solar System

Jupiter

The magnetic field of Jupiter is revealed by its
strong aurora.

Ultraviolet image of the Auroras on Jupiter from Hubble.
http://oposite.stsci.edu/pubinfo/PR/2000/38/content/0038w.jpg

Mars does not have a strong dipole magnetic field
and so does not have auroras circling its poles. However at one time
it had a strong magnetic field which was recorded in molten volcanic
rocks creating stripes like those due to continental drift on
earth.

Red and Blue stripes on Mars record an ancient Martian
magnetic field which changed its polarity.
http://mgs-mager.gsfc.nasa.gov/publications/grl_28_connerney/images/grl_28_connerney_cover_black.jpg

Sun

The sun has a strong magnetic field that reverses
polarity every 11 years creating the sunspot cycle.

Sunspots themselves have strong magnetic fields,
they come in pairs with a north pole spot next to a south pole spot.
The glowing solar plasma follows the field lines of sunspots creating
a pattern like the one produced by sprinkling iron filings onto a
simple bar magnet.

Glowing plasma follows the magnetic field of sunspots on the
surface of the sun.
http://vestige.lmsal.com/TRACE/Science/ScientificResults/trace_cdrom/html/trace_images.html